Cobalt-Coated Nickel Cathode Blend for Battery Cycle-Life Stability
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Solution Overview
Problem
Existing positive active materials for rechargeable lithium batteries suffer from structural collapse during repeated charges and discharges, leading to deteriorated long-term cycle-life and increased resistance, which limits their capacity and energy density.
Innovation Solution
A positive active material composed of a first nickel-based material with secondary particles formed by aggregated primary particles and a second nickel-based material with a single crystal form, both coated with cobalt, enhancing surface roughness and specific surface area, is developed through a three-stage heat-treatment process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional positive active materials (lithium nickel-based oxide, lithium nickel manganese cobalt composite oxide, etc.) are used, then high capacity and high energy density can be achieved, but structure collapses or cracks occur during repeated charges and discharges, leading to deteriorated long-term cycle-life and increased resistance
Solution Approach 1:
The positive active material is divided into two distinct components: first positive active material in the form of secondary particles (aggregates of primary particles) and second positive active material in single crystal form. Each component serves a specific function - the secondary particles provide high capacity while the single crystals maintain structural stability, resolving the contradiction between capacity and cycle-life through functional segmentation.
Solution Approach 2:
The invention creates a composite positive active material combining two different nickel-based oxide structures (secondary particles and single crystals) in specific weight ratios (30:70 to 70:30). This composite structure leverages the high capacity of secondary particles and the structural stability of single crystals, achieving both high capacity and long cycle-life simultaneously.
2Quantity of substance
If conventional positive active materials are used, then high capacity can be achieved, but resistance increases during repeated charges and discharges
Solution Approach 1:
By segmenting the positive active material into two components with different structural characteristics, the invention isolates the high-capacity function in secondary particles from the resistance-increasing problem. The single crystal component maintains low resistance during cycling, preventing the overall resistance increase that would occur with conventional materials.
3Quantity of substance
If nickel-based positive active materials are used to achieve high energy density, then capacity is improved, but structural stability deteriorates during repeated charges and discharges
Solution Approach 1:
The invention applies different structural qualities to different components: secondary particles with aggregated structure for high energy density, and single crystals with ordered structure for structural stability. Each component's local structural quality is optimized for its specific function, allowing the composite material to achieve both high energy density and structural stability.
Solution Approach 2:
The composite structure combines two nickel-based oxide forms with complementary properties. The secondary particles contribute high energy density while the single crystals provide structural stability, creating a material that achieves both objectives simultaneously through synergistic combination.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The material exhibits improved cycle-life characteristics, high capacity, and high energy density, with enhanced charge and discharge efficiency due to the cobalt coating on both materials, effectively suppressing structural collapse.
Implementation Method 1
both of the first positive active material and the second positive active material are coated with cobalt
Implementation Method 2
performing second heat-treatment to prepare a second nickel-based oxide
Data Source
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AI summary
Disclosed are a positive active material for a rechargeable lithium battery, a preparing method thereof, and a rechargeable lithium battery including the same. The positive active material includes a first positive active material in a form of secondary particles in which a plurality of primary particles is aggregated, and a second positive active material having a single crystal form, wherein both of the first positive active material and the second positive active material are nickel-based positive active materials, each of the first positive active material and the second positive active material is coated with cobalt, and a maximum roughness of the surface of the second positive active material is greater than or equal to 15 nm.